Uncaught ReferenceError: process is not defined

Webpack can inject environment variables into the “client side” .js code (very useful in case of SPA/PWA). You should define them as plugins in webpack.config.js

webpack.config.js

module.exports = {
plugins: [
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
      'process.env.MY_ENV': JSON.stringify(process.env.MY_ENV),
      ... and so on ...
    })
],
}

Now you can access it on client side:

app.js

// Something like that
if(process.env.NODE_ENV === 'debug'){
    setDebugLevel(1)
}